Could the bullet have have ricocheted off something and gone airborne for 5 miles? It is possible.
Military firing range safety is an area of my expertise. Army firing range safety is governed by Army Regulation 383-63 and DA Pam 385-63.
Go to the link. You are looking ar DA Pam 385-63. Look at Figure B-1, page 173 of DA Pam 385-63. You are interested in distance X for ground fired direct fire weapons: This is the maximum range. Got to page 175 and look at .50 caliber ball in the left hand column. Distance X is listed as 6,500 meters. This does not equate to five miles.
Warning to .50 caliber shooters:
The .50 caliber ball projectile will penetrate 152 inches of packed earth.
Did the police use the ground mileage to the firing range from the point of impact?